Function that returns updated values once every time period, no matter how often it is called

limiter.go

package main

import (
	"fmt"
	"time"
)

// This function returns a function that returns the current time. The current
// time is only updated when the returned function is called, and at most once
// during every period
func updater(period time.Duration, value func() interface{}) func() interface{} {
	v := value()
	wanted := make(chan bool)

	// Anonymous function that returns a function that returns a timer of the
	// duration requested (period). So every application of newtimer()
	// gets an alarm that will go off in 5 seconds
	newtimer := func(next time.Duration) func() <-chan time.Time {
		return func() <-chan time.Time {
			return time.After(next)
		}
	}(period)

	// Closure that returns the current value of v
	getvalue := func() interface{} {
		wanted <- true
		return v
	}

	// Go routine that updates the value of v when the timer expires (refresh is
	// set to true) and a request to know the value is made through the closure
	// ret (a message is sent through the channel c)
	go func() {
		refresh := false
		timer := newtimer()
		for {
			select {
			case <-timer:
				refresh = true
				timer = newtimer()
			case <-wanted:
				if refresh {
					v = value()
					refresh = false
					timer = newtimer()
				}
			}
		}
	}()

	return getvalue
}

func main() {
	v := updater(5*time.Second, func() interface{} { return time.Now() })
	for {
		time.Sleep(1 * time.Second)
		fmt.Println(v())
	}
}